The present invention relates to a tool for manufacturing louvered fins for a heat exchanger and a surface finishing method for the tool, and more particularly to a tool for manufacturing louvered center fins configured to achieve an improvement in heat exchange efficiency in a variety of heat exchangers. The present invention also relates to a method for finishing the surface of such a tool.
In an air conditioner equipped in vehicles, a heat exchanger serves as an interface for conducting a heat exchange of the air conditioner with ambient air. Such a heat exchanger is configured in various forms, for example, in the form of a condenser, a radiator, a heater core, or an evaporator.
Although there are a variety of heat exchangers, they have similar configurations. That is, most heat exchangers include a pair of header tanks for receiving a heat exchange medium introduced therein, and a plurality of parallel heat exchange tubes arranged between the header tanks in a stacked fashion and adapted to form an elongated flow passage for the heat exchange medium.
A louvered fin having the form of a sheet is interposed between adjacent ones of the heat exchange tubes while being bonded to those adjacent heat exchange tubes. For the bonding to the heat exchange tubes, the louvered fin is coated, at both surfaces thereof, with clad layers made of a fusible metal having a low melting point.
The louvered fin is bent in a zig-zag fashion to have a corrugated structure. In order to provide a maximized heat exchange efficiency, the fin is also provided with a plurality of,parallel louvers so that it has a louvered structure. The louvers are formed by cutting each flat wall portion of the fin at a plurality of positions along the length of the flat wall portion, and then bending those cut portions from the plane of the flat wall portion. By virtue of such a louvered structure, the fin has a maximum contact area with ambient air.
Since the above mentioned fin has a corrugated and louvered sheet structure bent in a zig-zag fashion and provided with a plurality of bent louvers, it is necessary to use a specific tool for the manufacture of such a fin.
Conventionally, such a tool includes a plurality of stacked parallel fin blades each provided at its periphery with a plurality of cutting teeth arranged in a pitch corresponding to the bending pitch of a fin to be formed. The number of the fin blades corresponds to the number of louvers to be formed at each flat wall portion of the bent fin.
In order to manufacture a louvered fin, a pair of tools having. the above mentioned arrangement are used. The tools are arranged adjacent to each other to define a nip therebetween. A metal sheet made of aluminum or clad-coated aluminum exhibiting a high thermal conductivity is forced to pass through the nip between the tools, so that it is simultaneously subjected to a bending process for the formation of corrugations in a zig-zag fashion and a cutting and bending process for the formation of louvers.
The fin blades of the tools are subjected to a severe using condition in that they are repeatedly and continuously used for the repeated and continued bending and cutting processes. For this reason, it is important to lengthen the life of the fin blades.
To this end, a variety of proposals have conventionally been made. For example, fin blades are manufactured using a high-speed steel thin plate which is subjected to a quenching process to have a Vickers hardness of 700 to 750 and then subjected to a surface treatment using a gaseous nitrification method.
However, conventional surface-treated tools used for the manufacture of louvered fins for heat exchangers have the following problems:
(1) The tools are easily abraded during the manufacture of louvered fins because they rotate at a high speed. For this reason, the tools should be periodically ground;
(2) Since the article to be machined by the tools is made of a metal, such as aluminum, exhibiting a high viscosity in most cases, burrs may occur at the tooth crests of the fin blades. As a result, a considerable degradation in workability occurs;
(3) In particular, where the clad metal of the fin is an alloy material containing Si, for example, a Alxe2x80x94Si-based or Alxe2x80x94Mnxe2x80x94Si-based composite material, the tools may be early abraded due to Si exhibiting a very high hardness;
(4) Since each tool uses a plurality of fin blades individually manufactured and then stacked together, it is very expensive. For this reason, a frequent replacement of such a tool results in a considerable increase in costs; and
(5) The frequent replacement and grinding of the tools cause a frequent temporary shut-down of the production line. Furthermore, the repeated grinding of the tools may result in a variation in the dimensions of louvered fins initially designed. As a result, it is impossible to manufacture louvered fins with an optimum heat exchange efficiency.
Therefore, the present invention has been made in view of the above mentioned problems involved in conventional tools used for the manufacture of louvered fins for heat exchangers and conventional surface finishing methods for those tools, and an object of the invention is to provide a tool for manufacturing louvered center fins, which has a maximized life, and a surface finishing method for the tool capable of allowing the tool to have a maximized life.
In accordance with the present invention, this object is accomplished by providing A tool for manufacturing louvered center fins of a heat exchanger and a surface finishing method for the tool, the tool including a plurality of fin blades each having a circular cutter shape and being provided at a periphery thereof with a plurality of cutting teeth and at a central portion thereof with a central hole, the fin blades being stacked on one another in such a fashion that the central holes are aligned together, and a pair of jig discs arranged at opposite sides of the stacked fin blades, respectively, in such a fashion that the jig discs are arranged in a coaxial and integral fashion with the fin blades, the tool serving to form louvered fins having a plurality of continued flat wall portions formed by bending a thin strip in a desired pitch in a zig-zag fashion, each of the flat wall portions having a plurality of louvers extending in perpendicular to the flat wall portion, wherein: respective crests of the cutting teeth in each of the fin blades are plasma-nitrified to a depth of 20 to 60 xcexcm, thereby forming a nitride layer on each of the crests; and depositing a coating of TiC, TiN, or TICN to a thickness of 2 xcexcm or less over the nitride layer in accordance with a plasma chemical vapor deposition method or a plasma physical vapor deposition method. Now, the tool for manufacturing louvered fins of a heat exchanger and a surface finishing method for the tool according to the present invention will be described in detail in terms of configurations, functions and effects, as compared with those of conventional cases.